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Retrogression and Re-Ageing (RRA) heat treatment is a newly innovated process to provide 7075 aluminum alloy with stress-corrosion resistance equivalent to T73 temper together with T6 strength levels. Due to the restriction of present process, this heat treatment can only be applied to thin sheet, while 7075 aluminum alloy is used primarily for thick sections.
This study is trying to obtain an optimum RRA heat-treatment process suitable for thick plate of 7075 aluminum alloy. The effects of retrogression time at 200℃, 190℃, 180℃ and 170℃ on Brinell hardness, electrical conductivity and crack growth rate of 25.4mm thick plate of 7075 aluminum alloy were studied.
Eperimental results show that T6 strength together with stree-corrosion resistance comparable to T73 temper can be achieved in 25.4mm thick plate of AA7075 by retrogressed at 200℃/30min , 190℃/80min, 180℃/5hrs 170℃/6.5hts during RRA heat treatment.
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